The present invention relates to pumps for sampling well water or water sites suspected of contamination and more particularly to pumps that are capable of both purging a well or water site prior to taking a sample.
Various types of pumps for the above purpose have been proposed, but for various reasons existing devices do not satisfy the diverse requirements of both purging and reliable sample taking. For example, many of the prior pumps that have been offered for sample taking include a rotating impeller that has the undesirable tendency to agitate or spin the water sample and destroy its efficacy. Other proposed pumps are based on air driven, alternately expanded and collapsed diaphragms that have some advantages, such as in isolating the water sample from the pump parts but is undesirable in the requirement of large, powerful air compressors at the well heads and in restrictions on the purging flow rate. Also, bladder type pumps tend to be limited to shallow wells and are susceptible to freezing up under certain operating conditions.
Hence, there is a need for a new pump design capable of the multipurpose operation suitable both for relatively large volume purging to enable rapid preparation of the bore hole prior to taking a sample, and for low volume flow sampling for delivering water samples that are not agitated, spun or otherwise disturbed from the natural state of the water as it existed in the undisturbed well hole. In providing such a multipurpose purging and sampling pump, it is also desirable to provide a construction that maintains isolation of the water samples taken from any source of contamination, and to be able to use a conventional, relatively power efficient well head drive source to operate the pump.